Film forming solution of cellulose acetate



Patented Mar. 1949 2,464,784 FILM FORMING SOLUTION or CELLULOSE CETATERussell P. Easton, Binghamton,

N. Y., asslg'nor to General Aniline & Film Corporation, New York, N. Y.,a corporation of Delaware No Drawing. Application August 9, 1945, SerialNo. 609,931

1 Claim. l This invention relates to the manufacture of sheets, films orfoils composed of cellulose organic esters and other film formingmaterials. More particularly, the invention relates to a method offacilitating the removal of such sheets, films, and foils from thesurface ,upon which they are cast. a

In the manufacture of sheets, foils, or films from high molecular, waterinsoluble film-forming materials such as cellulose organic estersranging from-.001 to .05 of an inch in thickness, and of any suitablewidth, the cellulose organic ester is dissolved in a suitable solventand a plasticizer added to make a composition which in the parlance ofthe trade is called a dope. This dope is cast on the surface of a slowlyrotating wheel or drum having a smooth nickel or chrome plated surface,or on the surface of an endless metallic band, and the solvents removedfrom the deposited material by means of heated air. Finally, thedried'or cured material is stripped from the casting surface in the formof a continuous sheet which is wound upon a shaft for storage or furtheruse, such as for coating with emulsions to form photographic film.Notwithstanding that the bulk of the solvent has been removed from thefilm when it reaches-the point where it. is

stripped from the casting surface, difliculty is experienced in theremoval of the material from the casting surface. In some instances,depending upon the nature of the plasticizer employed, the cast film orfoil adheres so tightly to the casting surface that it requiresconsiderable force to remove it. This causes the film to strip off in anunsteady manner with considerable jerking. Vibrations are set up-and thesurface of the film or foil develops crosswise markings which distinctlyimpairthe quality of the' resulting product. The adhesion may be sogreat in some cases as to cause small portions of the film to be tornaway from the main body of the material and left upon the castingsurface.

In order to obviate the above difliculties, it has been suggested thatconsiderable care be exercised in selecting the plasticizer for thecellulose organic ester. The plasticizer selected should be of a highboiling point so that it will remain in the foil at the end of thedrying span. For photographic film, the plasticizer selected must bephotographically inert and resistant to hydrolysis. It must not lowerthe flexibility nor increase the water sensitivity of the film or foil.The plasticizers which are generally suggested for use by the art inthis connection are, for ex-, ample, triphenyl phosphate, trinaphthylphos- 2 phate', tricresyl phosphate, tricresyl thiophosphate, naphthyldiamyl phosphate, trixylyl phosphate, dlmethyl phthalate, isobutylphthalate,

dibutyl phthalate, methyl cyclohexyl acetatephthalate, methylphenoxyethyl phthalate, acetyl tributyl citrate, tributyl citrate,hydrophthalic acid diethyl ester, octyl phenyl ether, orthophthalic aciddiethyl ester, mixtures of oand .p-toluene ethyl suifonamides and thelike. It is possible by selecting a plasticizer from this group tocorrelate its properties and the amount used with the particularcellulose ester employed, to obtain foils or films which have therequisite tensile strength to furnish pliability and the like. However,despite the care exercised in selecting such plasticizers andirrespective of the improvements obtained in the physical properties bythe use thereof, the diiiiculty in stripping the film or foil from thecasting surface is not overcome. The principal object of the presentinvention is to avoid the above mentioned difficulties and to provide ameans whereby such films, sheets, or foils may be stripped from acasting surface with ease and without impairment of their quality.

Another object is to provide an improved method of stripping celluloseorganic esters and other film-forming substances from a casting surface.

These and further objects will become apparent in the followingdescription.

1 I have discovered that I am enabled to achieve the objects of thepresent. invention by selecting a combination of plasticizers which notonly acts as a plasticizer for the film-forming material and imparts theaforesaid desirable physical characteristics thereto, but also aids inthe stripping of the cast film or foil after drying or curing. Thiscombination consists of a mixture of a trialkyl phosphate and a commonplasticizer which is normally. employed in plasticizing celluloseorganic esters.

Any trialkyl phosphate may. be employed pro- "vided, however, that eachalkyl group therein contains at.least 5 carbon atoms. Examples ofsuitable phosphates are triamyl phosphate, tripentyl phosphate, trihexylphosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate,triclecyl phosphate and the like. The plasticizing agent generallyemployed in plasticizing cellulose esters which with the trialkylphosphate is critical to the success of the invention is exemplified bytriphenyl phosphate, trinaphthyl phosphate, tricresyl phosphatefdioctylphosphate, tricresyl thiophosphate, trixylyl phosglycol di-2-ethylhexoate, triethylene glycol di- 2-ethyl butyrate and the like.

The mixture of the aforesaid components is added directly to the highmolecular weight filmforming material, to the solvents employed indissolving the same, or to the solution of said film-forming material ina suitable solvent or solvent mixture. The amount of trialkyl phosphateemployed is in the ratio of 0.5 to 3 parts by weight to approximately 3to 5 parts by weight of any common plasticizer for each 10 to 20 partsby weight of the film-forming material. The most desirable ratio ofplasticizer mixture, however, is 0.8 part by weight of trialkylphosphate to 3.2 parts by weight of the common plasticizer for each 16parts by weight of the film-forming material.

The use of trialkyl phosphates alone renders the plasticizedfilm-forming dope unsuitable for casting purposes. The partially driedor cured foil or film does not adhere sufllcientiy to the casting drumbeforethe drum or other circular casting means has made a completerevolution to the guide roll which leads to a'drying chamber. As aresult thereof, the partially dried film or foil slips from the undersurface of the casting drum and falls to the ground. on the other hand,the commonly used plasticizers when employed per se lead to animpairment of the film and.strip. However, by the combined effect ofboth on the film-forming materialythe desired result is achieved. Justhow each component of the plasticizing m xture contributes to theunitary action has not been ascertained. That both cooperate by exertinga definite influence on each other and on the high molecular weight filmforming material, however, is not open to dispute.

The trialkyl phosphates employed in accordance with the presentinvention are prepared by reacting a phosphorous oxyhalide, e. g.,phosphorous oxychloride with a hydroxy alkyl compound such as, forexample, n-amyl alcohol, isoamyl alcohol, 2-pentanol, 3-pentanol, d-amylalcohol. amylene hydrate, l-hexanol, 2-hexanol, 2 methyl l-pentanol,3,3-dimethyl-2-butanol, 2,3-dimethyl-2-butanol, l-heptanol, l-octanol,l-nonanol, l-decanol, and the like, and have the following generalformula:

R--O-P=O R-O/ wherein R is an alkyl group ranging from to carbon atoms.

The trialkyl phosphates having the foregoing general formula areavailable commercially and inmost instances are viscous oils'or solidresins at room temperature. They are readily soluble in the highmolecular weight film-forming materials and in most normally liquidsolvents such as alcohols, i. e., methyl, ethyl, propyl, butyl, amyl andthe like, and ketones such as acetone, methyl ethyl ketone, diethylketone, and the like, aromatic hydrocarbons such as benzene, toluene,xylene and the like, and chlorinated hydrocarbons such as chiorobenzene,chloroform, methy lene chloride, chlorinated kerosene and their mixtureswith alcohols and ketones asabove and esters such as dibutyl acetate,diamyl acetate, cellosolve commonly used in lacquer solvents.

In practicing the present invention. any unplasticized film formingmaterial may be employed, such as a cellulose organic ester. forexample, cellulose acetate. cellulose formate. cellulose propionate,cellulose butyrate, cellulose acetate-propionate, celulose'acetate-butyrate. and the like, or cellulose nitrate, or film-formingpolymers, such as polyvinyl chloride, copolymers of vinyl chloride-vinylacetate, copolymers of vinyl chloride-vinylidene chloride, polyamides,superpolymers and the like.

The nature of the solvent or solvent mixture employed in preparing dopesof the above-listed cellulose organic esters and film-forming polymersis immaterial so long as it dissolves or is compatible with theplasticizing mixture of the present invention. This fact can beascertained readily by a simple experiment.

For a fuller understanding of the nature and objects of the invention,reference is made to the following examples which are given merely tofurther illustrate the invention, and they should not be regardedaslimiting it. All the parts are by weight.

Example I A solution or dope is made up as follows:

- Parts Cellulose acetate (containing 58% acetic acid) l6 Trioctylphosphate 0.8 Triphenyl phosphate 3.2 Methyl alcohol 8.0 Methylenechloride 72 This solution was cast upon the polished periphery of a drumto form a layer which upon drying would produce a film of about 0.008 ofan inch in thickness. The partially dried film was removed with easewhen taken up by the guide roll leading to the drying chamber.

The advantages of the invention were brought home by contrasting theabove procedure with the following, illustrating the effect of adding acommon plasticizer to a cellulose organic ester dope from which a filmis cast.

7 Parts Cellulose acetate (containing 58% acetic acid) 16 Triphenylphosphate 4 Methyl alcohol 8 Methylene chloride 72 Example 11 PartsCellulose acetate-propionate 20 Triamyl phosphate 1.2 Tricresylphosphate 4.0 Acetone 75 Example III 4 Parts Copolymer of vinylchloride-vinyl acetate Tridecyl phosphate 0.6 5 Dibutyl phthalate 2.8Methyl alcohol 8.0 Methylene chloride 1 80 The solutions of Examples IIand III when cast resulted in satisfactory films, which were 10 readilyremoved and did not possess any undesirable characteristics.

It is evident that the solutions or dopes prepared in accordance withthis invention are not limited for casting on a peripheral surface, but

are also capable of being cast on endless metallic belts to give films,foils, or sheets which are clean ly stripped from the casting surface.

While the present invention-has'been described in considerable detailwith reference to preferred procedures and materials, it is to beunderstood that the invention is not limited thereto and that numerousvariations may be made in the procedures herein described. All suchmodifications and variations are within the scope of the invention asdefined by the appended claim.

Iclaim:

A film-forming solution or cellulose acetate consisting essentially ofabout 16 parts of cellulose acetate, an organic solvent therefor in anamount suitable for strip casting, about 1 part of trioctyl phosphate,and about 4 parts of triphenyl phosphate.

' RUSSELL P. EASTON.

REFERENCES orrnn The following references are of record in the file ofthis patent:

'UNITED STATES PATENTS

